In a vehicle during turning at an intersection or a winding road, inertial forces act on a body of a seated occupant. When the body is not stabilized due to such inertial forces, the seated occupant should have an uncomfortable ride. In particular, when the body of a driver is not stabilized, the driver is required to pay greater attention for driving operation, which makes it hard to have a comfortable ride. For this reason, the prior art has proposed various seat structures configured to stably support a seated occupant during turning of a vehicle.
For example, Patent Documents 1 and 2 teach seat structures configured such that side supports of a seat cushion slidingly move vertically or rotate up and down about respective axes extending in a right-to-left direction to properly support a seated occupant. Patent Document 3 discloses a seat structure in which side supports rotate about respective axes in a front-to-rear direction (longitudinal direction) to support a seated occupant in a vehicle during turning of the vehicle. Patent Document 4 discloses a structure configured to properly support a seated occupant by changing an orientation of a seat back toward a turning direction during turning of a vehicle.